Wavelength division multiplexing (WDM) systems typically comprise multiple, separately modulated, optical carrier signals, each one being assigned to a different channel slot, or frequency, in the WDM signal. The sources for the carriers can be located at a single head-end in long-haul applications or remote from each other, with the channels typically being accumulated onto a single fiber by multiplexers, in metro area network applications, for example. Along the fiber transmission link, the carriers can be regenerated or collectively amplified typically by gain fiber, semiconductor optical amplifiers (SOA), or doped waveguide devices. At the link termination, the carriers are usually demodulated or separately routed to new links.
Spectral information is required to confirm the proper operation of WDM systems. Generally, the types of information required are different depending on the type of system. Long haul systems are many times concerned with information such as the spectral shape of the channels and optical noise level. Optical signal to noise ratio (OSNR) is a common metric that is required by these systems. The spectral information is used to control the amplifiers and possibly correct for any gain tilt. Networks that possibly include add-drop or cross-connect devices are typically interested in channel slot occupancy information, i.e., whether or not a carrier signal is present in a given channel slot. They also typically monitor whether or not specific carriers are located to their assigned channel slot frequency and/or whether or not they are operating at the correct power level.
The speed at which the WDM systems require spectral information is different. Confirmation of correct channel routing, fault recovery, and excessive channel power must sometimes be detected quickly. Preferably, a fault, for example, should be detected in a few milliseconds or less. In contrast, noise floor information and the channel spectral shape typically change much more slowly. As a result, some long haul WDM systems can wait for over a second to obtain some types of information.
The present invention is directed to a system and method for fast peak finding in an optical spectrum. The system is capable of prioritizing the information it first generates and how the information is then forwarded to a network controller, such as a host computer. It is able to very quickly find some information, such as whether or not channels or carriers are present, at what frequency the carriers are operating, and the carriers"" power level and send this information to the host computer. In contrast, information concerning spectral shape or the noise floor is sent later in time.
In general, according to one aspect, the invention features an optical spectrum monitoring system. It comprises a spectrum detection subsystem for generating a spectrum of an optical signal. An analog-to-digital converter converts the spectrum into sample data. A data processing subsystem first detects the spectral locations of peaks in the spectrum using the sample data and then uploads the peak information to a host computer before completing processing to determine the shapes of the peaks and/or noise information for the optical signal, for example.
In the current embodiment, the spectrum detection subsystem comprises a microelectromechanical system (MEMS) tunable filter. A reference source is sometimes provided for calibrating the spectrum detection subsystem.
Also, according to the present embodiment, the data processing subsystem uploads the sample data to the host computer before uploading the peak information to the host computer. Further, to facilitate fast peak detection, the data processing subsystem begins detecting the spectral locations of the peaks even before the completion of the conversion of the spectrum into the sample data, i.e., the scan is completed.
According to the present implementation, the data processing subsystem comprises a processor that includes a processor core and at least two blocks of processor memory. A system memory is also provided. The blocks of processor memory are used as a xe2x80x9cping-pongxe2x80x9d buffer to transfer data from an analog-to-digital converter to the system memory.
In order to enable the beginning of the processing of the sample data, even while the sample data are being collected, direct memory addressing is used to transfer the sample data from the processor memory to the system memory, thereby allowing the processor core to calculate the peak information. Additionally, the processing subsystem also generates calibrated sample data from the sample data in response to calibration information and then uploads the calibrated sample data to the host computer. Preferably, also, the data processing subsystem deconvolves a filter transfer function from the spectrum of the sample data to generate a corrected spectrum.
In general, according to another aspect, the invention also features a method for processing spectrum data in an optical spectrum monitoring system. This method comprises detecting a spectrum of an optical signal and converting the spectrum into sample data. The spectral locations of peaks in the sample data are then detected. This peak information is uploaded to a host computer. Finally, after at least beginning the step of uploading the peak information, the shapes of the peaks and/or noise information are determined for the optical signal.
In the preferred embodiment, sample data are uploaded to the host computer before the peak information is uploaded. The step of detecting the spectral locations of the peaks is started before completion of the step of converting the spectrum into sample data.
The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention.